Means of controlling the emptying of tanks containing liquids of different density



Sept. 9, 1958 E. D. HOBSON 2,851,193

' MEANS OF CONTROLLING THE EMPTYING OF TANKS CONTAINING LIQUIDS OF DIFFERENT DENSITY Filed Sept. 4, 1956 2. E a) N a .J

INVENTOR ATT RNEYS United States Patent Eric Dott Hobson, Shandon, Scotland, assignor to Yarrow and Company Limited, Scotstoun, Glasgow, Scotland Application September 4, 1956, Serial No. 607,727

Claims priority, application Great Britain September 8, 1955 4 Claims. (Cl. 222-66) This invention relates to means for controlling the emptying of a tank or the like containing two stratas of normally non-miscible liquids of different density and more particularly to means for ensuring that the strata of liquid of greater density, settled at the bottom of the tank or the like, may be drawn 0E and the strata of liquid of lower density, floating on the surface of the other liquid, left in the tank.

The invention is particularly applicable to emptying tanks normally used in ships for storing fuel oil, the tanks being adapted to be filled with sea water for ballasting purposes when thefuel oil has been drawn oil and used. In this case a residue of oil will remain when the tank is filled with sea water and form a strata floating on the surface of the water. When it is desired to empty the tank of sea water before refilling it with oil it is usual to pump the water overboard, but it is essential that the pumping operation should not be continued after the level in the tank has fallen to a point where there is a danger that the strata of oil or oil contaminated water may be pumped from the tank, and that the pumping operation be slowed down when approaching the desired level in order to prevent the carry-over of the strata of oil by vortices tending to form above the pipe inlet.

According to the present invention apparatus for controlling the emptying of a tank containing two stratas of normally non-miscible liquids of different density includes a suction conduit having its inlet disposed adjacent to but spaced from the bottom of the tank and an air pipe located within said suction conduit and provided with an outlet disposed at a predetermined distance from the bottom of the tank, said distance substantially corresponding to the depth of the upper of the stratas of liquid, the arrangement being such that when the lower of the stratas of liquid has been withdrawn or substantially withdrawn from the tank through the suction conduit, air from said air pipe will be drawn into the suction pipe so as to destroy its suction effect and prevent further liquid being drawn from the tank.

To enable the invention to be fully understood it will now be described with reference to the accompanying drawing which illustrates in diagrammatic form one em 'bodiment of the invention.

As shown in the accompanying drawing 1 indicates an oil fuel storage tank of a ship which is adapted when emptied of oil to be filled with water for ballasting purposes.

A suction conduit 2 extends in a fluid tight manner through the vertical wall a of the tank, the conduit including a down-turned portion 3 extending Vertically towards "me bottom of the tank and having an inlet disposed adjacent to but spaced from the bottom b of the tank. As shown the inlet of the suction conduit is flared outwardly to form a bell mouth 4. It will be understood that the conduit 2 will be connected in known manner with a suction pump (not shown).

An air pipe 5 extends vertically through the tank, its upper end projecting in a fluid tight manner through the Patented Sept. 9, 1958 top wall 0 and being connected through a control valve 6 with a pipe 7 communicating with atmosphere. The pipe 5 extends vertically downwardly through a tubular extension 8 located adjacent to a side wall of the downturned portion 3 of the suction conduit, suitable fluid tight packing means 9 being provided.

It will be noted that the air pipe extends coaxially through the down-turned-portion 3 its lower open end terminating adjacent to but spaced inwardly of the open end of the bell mouth 4.

As shown the air pipe is provided with a series of axially spaced apertures 5a, the lowermost of which is disposed at a distance from the bottom wall b of the tank which distance is substantially equivalent or slightly above the depth of the strata of oil which will be floating on the ballast water of the tank, that is to say said lowermost aperture will be disposed at or slightly above the minimum level at which it is desired to stop pumping to prevent the upper strata of oil being withdrawn through the suction conduit.

Assuming that the tank 1 has been filled with sea water to replace fuel oil originally contained in the tank, the quantity of oil thereafter contained in the tank will comprise the residue left in the tank below the level of the bell mouth 4, plus the quantity of oil that was adhering to the internal walls of the tank. In consequence the depth of the strata of oil and the level at which pumping should stop to prevent carry-over of oil or oil contaminated water can be defined in practice.

When the sea water is to be discharged from the tank to enable it to be refilled with oil, a pump is set in operation to draw oil the water through the suction conduit, the water being discharged overboard. As the said minimum level of liquid is approached a sub-atmospheric pressure will be induced within the lower end-of the conduit 3 and accordingly air will be drawn in through the uppermost of the apertures 5a of the air pipe and this air will, by replacing the flow of water,'have the elfect of slowing down the pumping operation. As the pumping is continued, however, the other apertures So will be progressively uncovered with the result that progressively increasing amounts of air will be drawn in the suction conduit and eventually the suction will be broken and further withdrawal of liquid prevented when substantially all the water has been drawn oil. Accordingly the strata of oil or oil contaminated water will be prevented from being sucked up through the conduit 3 and drawn oil from the tank.

This strata of oil and oil contaminated water can be subsequently drawn ofr" preferably by a separate pumping system which may make use of the same suction conduit after adjustment of the appropriate conduit valves and after the valve on the air pipe external to the tank has been closed. Alternatively a separate suction conduit may be provided located at the lowest point of the tank and delivering to a suitable container and thereafter treated to separate the oil.

The height above the base of the tank at which the lowermost of the apertures 5a is located determines the said minimum level but it is not necessarily coincident with that level.

lclaim:

1. Apparatus for controlling. the emptying of a tank containing two strata of normally non-miscible liquids of diflerent densities, which apparatus comprises a downwardly extending suction conduit through which liquid is withdrawn, said conduit having its inletdisposed adjacent to but spaced from the bottom of the tank, and an air pipe terminating at one end within the suction conduit and communicating with the atmosphere outside the tank at the other end, said pipe having a discharge opening in the end within the conduit spaced a predetermined distance from the bottom of the tank, said distance substantially coyresponding to the depth of the upper of the liquid strata, whereby when the lower of the liquid strata has been substantially withdrawn from the tank through the suction conduit air from said airpipe will be drawn into the suction conduit so as to destroy the suction effect and prevent further liquid being withdrawn from the tank.

2. Apparatus according to claim 1 wherein said air pipe is connectable at its other end with the atmosphere through a valve.

3. Apparatus for controlling the emptying of a tank containing two strata of normally non-miscible liquids of different densities, which apparatus comprises a downwardly extending suction conduit through which liquid is withdrawn, said conduit having an inlet end disposed adjacent to but spaced from the bottom of the tank, an air pipe extending axially within said suction conduit and having a lower end portion provided with a series of axially spaced air discharge ports each opening into said suction conduit, the discharge port nearest to the lower end of said air pipe being spaced from the bottom of the tank a distance substantially equal to the depth of the upper of said strata of liquid.

4. Apparatus for controlling the emptying of a tank containing two strata of normally non-miscible liquids of ditferent densities, which apparatus comprises a downwardly extending suction conduit through which liquid is withdrawn, said conduit having an inlet positioned adjacent to but spaced from the bottom of the tank, a vertically disposed air pipe disposed within said suction conduit and having a lower end portion provided with axially spaced air outlet means, the part of said air outlet means nearest to the extreme lower end of the air pipe being spaced from the floor of the tank a distance substantially equal to the depth of the upper of the liquid strata so that said outlet means will be progressively uncovered to allow air to enter the suction conduit as the final part of the lower of the liquid strata is withdrawn from the tank through said conduit.

References Cited in the file of this patent UNITED STATES PATENTS 2,627,366 Glick -n Feb. 3, 1953 

